Latest figures from Revenue show that 19 offensive weapons were recovered in Sligo, where none were found last year.
Nine weapons were found at Dublin Airport, a figure believed to include the discovery of loaded pistols in the luggage of an elderly woman in April of this year.
In addition, 17 offensive weapons were recovered at the Dublin Mail Centre, more than in the whole of last year.
Two firearms were found at Portlaoise Mail Centre, in addition to two offensive weapons. Four offensive weapons were found in Cork, and two were intercepted at Shannon Airport.
Last year, 74 firearms were seized by Customs, as well as 181 offensive weapons.
According to a Revenue spokesman, offensive weapons include flick knives and machetes.
While Customs officers continue to monitor weapons being sent through the post, it has also emerged that the amount of drugs intercepted in the postal system has also grown.
Officials expect to seize more than one million prescription drug tablets by the end of the year, after successive annual increases in the number of pills intercepted in recent years.
Among the main drugs being sent in the post is oxycontin, a painkiller which can be addictive.
According to principal officer, Michael Colgan, prescription drugs are now matching the trade in illegal drugs. “Most shipments are concealed in postal shipments from Malaysia, Thailand and Pakistan.”
Earlier this year a study by Pfizer found that the counterfeit medicines market in Ireland could be worth more than €86m a year.